(1) Field of the Invention
This invention relates to novel alkenylphenylmaleimide derivatives and linear dimers thereof which have high thermal decomposition temperatures, exhibit rapid curability, and are easily soluble in common organic solvents. In another aspect, it relates to a process for the preparation of such maleimide compounds.
(2) Description of the Prior Art
A variety of heat-resistant resins have been developed as insulating materials meeting the constant demands for greater capacity, miniaturization and weight-saving, improved reliability and thermal stability, longer lifetime, maintenance-free properties, etc. of electronic devices and apparatus. Generally, bismaleimides (including N,N'-(methylenedi-p-phenylene)bismaleimide as a typical example) obtained by reacting a primary amine with maleic anhydride provide thermosetting resins having excellent heat resistance and a dense structure. However, these maleimides are high in melting point and sparingly soluble in common organic solvents. Accordingly, if it is desired to use them in the form of a solution, they must be dissolved in high-boiling polar organic solvents, such as dimethylformamide, dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, etc., that are undesirable for reasons of safety and health. Moreover, when an impregnating varnish prepared by reacting such a bismaleimide with a diamine and dissolving the resulting prepolymer in dimethylformamide or N-methylpyrrolidone is used in the fabrication of copper-clad laminates, removal of the solvent is so difficult that gas bubbles, blisters of the copper foil, and other defects may develop. Because of this great technical disadvantage, the needs of the times have recently changed from impregnating varnishes of the solution type to ones of the solventless type. In order to solve the above-described problems, there have been proposed, for example, a method of modifying poly(phenylmethylene)polymaleimide by incorporating an epoxy resin thereinto (Japanese Patent Laid-open No. 21098/'75) and a method of modifying a prepolymer of a bismaleimide and a polyamine by incorporating an epoxy resin thereinto (Japanese Patent Publication No. 27519/'75). In these modified maleimide compositions, however, the maleimide tends to precipitate at temperatures in the vicinity of room temperature and the limitation placed on the maleimide content prevents the achievement of satisfactory heat resistance and adhesion properties. Thus, they are not suitable for practical use as industrial materials required to have high performance.
In the prior art, processes for preparing maleimides, bismaleimides, and polymaleimides are well known and one example thereof is disclosed in U.S. Pat. No. 4,130,564. However, the maleimide compounds of the present invention cannot satisfactorily be prepared according to this process. Specifically, since the maleimide compounds of the present invention have high solubility in organic solvents and great affinity for organic solvents, they cannot sufficiently be crystallized by cooling the reaction mixture after completion of the maleimide-forming reaction. Moreover, if a bad solvent such as water or the like is used to precipitate the formed maleimide compound (alkenylphenylmaleimide derivative or linear dimer thereof) from the reaction mixture, the maleimide compound undergoes a marked degree of agglomeration and fails to remain in the form of particles of proper size. Furthermore, the maleimide compound precipitated by a large amount of bad solvent is a very impure product containing various by-products and must therefore be purified by recrystallization from a special organic solvent such as acetonitrile or the like. Thus, the prior art fails to provide a technologically simple and industrially advantageous process for preparing the maleimide compounds of the present invention.